Burst-mode laser control circuit and the method thereof

Abstract

A burst-mode laser control circuit and related methods thereof are disclosed. Using an APC loop with an additional burst-mode control circuit, and a switch in series with a diode and in parallel with the laser, a continuous-mode laser driver is enabled to operate in burst-mode by turning the switch on or off via external logic. Burst-mode control manages the switch, and a bandwidth-select circuit using a high or low logic level input, wherein the laser is disabled and the bandwidth-select circuit enters a fast-track mode when the external logic signal has a first level. The laser provides regular optical signals, and the bandwidth-select circuit enters a slow-track mode, thereby enabling the APC loop to operate normally, when the external logic signal has a second level. In addition to a low cost and simple implementation, the control circuit and method provide lasers with a fast response capability using one or more externally-controlled switch circuits to meet demands of PON systems for burst-mode ONUs.

What is claimed is: 
     
       1. A burst-mode laser control circuit, comprising:
 a) an automatic power control (APC) loop; 
 b) a laser; 
 c) a diode; and 
 d) a burst-mode control circuit comprising a switch in series with the diode and parallel to the laser, the switch being enabled or disabled by external logic, thereby providing burst-mode control of the laser. 
 
     
     
       2. The burst-mode laser control circuit of  claim 1 , wherein said switch and said bandwidth-select circuit are enabled or disabled with a high or low logic level input. 
     
     
       3. The burst-mode laser control circuit of  claim 2 , wherein said bandwidth-select circuit comprises a high-low bandwidth-select circuit and a delay circuit. 
     
     
       4. The burst-mode laser control circuit of  claim 3 , wherein said high-low bandwidth-select circuit comprises has a fast-track mode and a slow-track mode. 
     
     
       5. The burst-mode laser control circuit of  claim 4 , wherein said switch disables the diode and the bandwidth-select circuit enters fast-track mode when the external logic provides a high logic level, and the laser provides optical signals and the bandwidth-select circuit enters a slow-track mode when the external logic provides a low logic level. 
     
     
       6. The burst-mode laser control circuit of  claim 4 , wherein said delay circuit comprises delay control logic configured to operate the APC loop in the fast-track mode before enabling the laser, and operate the APC loop in the slow-track when enabling the laser to operate. 
     
     
       7. The burst-mode laser control circuit of  claim 6 , wherein said delay control logic enables the APC loop to control power to the laser before the laser is enabled, thereby providing a stable laser power output when the laser begins to operate. 
     
     
       8. The burst-mode laser control circuit of  claim 1 , wherein the APC loop comprises the laser, a continuous-mode laser driver, and the bandwidth-select circuit. 
     
     
       9. The burst-mode laser control circuit of  claim 1 , wherein the laser comprises a burst mode laser. 
     
     
       10. The burst-mode laser control circuit of  claim 9 , wherein the burst mode laser comprises a distributed feedback (DFB) laser or an electro-amplitude modulated laser (EML). 
     
     
       11. The burst-mode laser control circuit of  claim 9 , further comprising a continuous mode laser driver, receiving a control signal from the APC loop and providing a driving signal to the laser. 
     
     
       12. A method of controlling a laser having a burst mode, comprising:
 a) when a logic input to an optical network unit (ONU) in a passive optical network (PON) has a first logic state, placing a bandwidth-select circuit in a fast-track mode for a predetermined period of time and disconnecting a switch, the ONU including the switch, a laser, a laser driver, a diode and the bandwidth-select circuit; 
 b) after the predetermined period of time, driving the laser using the laser driver and transmitting an optical signal from the laser normally; 
 c) when the optical signal from the laser is stable, placing the bandwidth-select circuit in a slow-track mode; 
 d) when the logic input to the ONU has a second state, turning on the switch to disable the optical signal from the laser and connect the laser in parallel with the diode; and 
 e) placing the bandwidth-select circuit in the fast-track mode when the logic input has the first logic state again. 
 
     
     
       13. The method of  claim 12 , wherein the first logic state is a low logic level, and the second logic state is a high logic level. 
     
     
       14. The method of  claim 12 , wherein the predetermined period of time is about 20 ns. 
     
     
       15. The method of  claim 12 , wherein after said logic input transitions to the second state, the bandwidth-select circuit stays in the fast-track mode for the predetermined period of time. 
     
     
       16. The method of  claim 12 , wherein placing the bandwidth-select circuit in the slow-track mode keeps optical signals from the laser stable. 
     
     
       17. The method of  claim 12 , wherein decreasing a voltage/current at a cathode and an anode of the laser results in no optical signal from the laser.